1. Field of the Invention
The present invention relates to a method of evaluating the quality of an image, a device for assisting in evaluating the quality of an image, an image forming device, and a computer program product for implementing the method of evaluating the quality of an image.
2. Description of the Related Art
Printed images and images loaded into a computer or the like via a scanner or from a digital camera contain defects that are called noises. The image noise (hereinafter referred to as a noise) is a cyclical variation in an optical characteristic (hue, brightness, saturation, or the like) occurring irrespective of an original image. In images, various noises occur depending on the performance of a printer that prints the images, that of the scanner via which the images are loaded, or that of the digital camera from which the images are loaded. For example, a noise that is short in the cycle of a variation in the optical characteristic (hereinafter referred to as a high-frequency noise) or a noise that is long in the cycle of a variation therein (hereinafter referred to as a low-frequency noise) may occur. Moreover, noises may occur linearly or circularly. In any case, an image containing many noises is recognized as an image of poor quality when it is viewed by human beings.
A known method is such that the foregoing noises are detected by performing Fourier analysis on an image to evaluate the quality of the image. According to the method of evaluating the quality of an image, zones having a predetermined shape are delineated in an image, and sampling points are disposed within the delineated zone. Thereafter, the positions of the sampling points are identified and optical characteristic values thereof are detected. The optical characteristic to be detected may be any of various optical characteristics, that is, a hue, brightness, and saturation. After the optical characteristic values of the respective sampling points are detected, Fourier analysis is performed on data items each representing the identified position and optical characteristic value of each sampling point to detect noises in respective zones. After noises are detected, the image quality of respective zones is assessed based on the noises. Consequently, the quality of the image is evaluated based on the image qualities of respective zones. When the quality of an image is evaluated as mentioned above, noises can be detected and the quality of the image can be evaluated.
According to the conventional method of evaluating the quality of an image, a parameter concerning a zone to be delineated in an image, that is, a shape or a size is predetermined but will not be changed. Moreover, a parameter concerning a distribution pattern of sampling points, that is, positions of sampling points, a distance between adjoining sampling points, and the number of sampling points are also predetermined but will not be changed. Zones are delineated in the same manner for any image and sampling points are disposed within each zone in the same manner for any image to evaluate the quality of the image.